The present disclosure relates to a power supply apparatus using a battery and a power supply switching method.
In recent years, secondary batteries, such as lithium-ion batteries, have rapidly found extensive application in power storage apparatuses for storing electric power, storage batteries for vehicles, and the like which are combined with new energy systems, such as solar batteries and wind power systems. In order to generate high output power, when many power storage elements, for example, unit batteries (also called battery cells, electric cells, or cells) are used, a configuration is employed in which a plurality of power storage modules are connected in series. A battery block is configured such that a plurality of battery cells, for example, four battery cells, are connected in parallel and/or in series. A power storage module (also called an assembled battery) is configured such that many battery blocks are housed in an exterior case.
There is a power storage system in which a plurality of power storage modules are connected and a control device common to the plurality of power storage modules is provided. A configuration is provided in which each power storage module has a module controller and communication is performed between the module controller and the control device via a communication device.
When the power storage system is used as a power supply, in some cases, a power storage module has to be switched to a backup power storage module even during flow of current. Because it is difficult to turn off, for example, an emergency power supply or a power supply of a base station for mobile phones, switching between the power storage modules is performed during flow of current. However, when batteries that are different in terms of the amount of charge are connected with each other, a large current exceeding a rating flows from a battery having a large amount of charge into a battery having a small amount of charge, and such a current may damage a power storage module.
In terms of switching a power supply to a backup power supply, techniques disclosed in Japanese Unexamined Patent Application Publications Nos. 2002-095173 and 2005-176461 have been suggested in the related art. In the technique disclosed in Japanese Unexamined Patent Application Publication No. 2002-095173, the outputs of two batteries are each connected to a common power supply circuit via a field-effect transistor. When a battery is accidentally disconnected in a state in which power is supplied from the battery to a load, the state is switched to a state in which power is supplied from the other battery to the load.
In the technique disclosed in Japanese Unexamined Patent Application Publication No. 2005-176461, when power supply trouble occurs in a load device operated by direct-current power, direct-current backup power is supplied. There are provided battery packs that each include a plurality of secondary batteries connected in series so that a voltage necessary for the load device is obtained. The life of each battery pack is determined and, when it is determined that a battery pack reaches the end of its life, only that battery pack is taken off and replaced.